Pre-oculomotor neurons in the superior colliculus, reticular formation, medial longitudional fasiculus, brachium conjunctivum, and Y-group of the vestibular nuclei will be studied with intracellular and intraaxonal recording techniques in anesthetized and alert squirrel monkeys. In anesthetized animals selected neuronal somata, electrophysiologically identified by anti- and orthodromic stimulation will be injected with horseradish peroxidase (HRP) for subsequent histological study and reconstruction at the light microscopic level. These same and other neurons will be studied in alert, trained, behaving animals. For alert animal studies eye movements will be measured using the magnetic search coil technique and natural and electrial stimulation of the vestibular system will be employed. Intraaxonal recordings will be taken to correlate neuronal firing patterns with eye movements and vestibular stimulation. (Computer aided analysis will be used on- and off-line). After physiological identification selected axons will be injected with HRP for subsequent reconstruction and characterization of axonal trajectories, patterns of collateralization and terminal fields at the light microscopic level. We thus hope to continue to provide structure-function correlation for the pre-oculomotor and oculomotor neurons so well studied at the extracellular level by others in this field. Our data, obtained from real neurons, will serve to evaluate the validity of existing and new models and concepts of oculomotor function.